Selector system for radio receiving apparatus



Aug. 14, 1934. 1.. JONES SELECTOR SYSTEM FOR RADIO RECEIVING APPARATUS 2 Sheets-Sheet 1 Filed Dec.

COUPLING CONTROL TUNING CONTROL il illa l1 OUTPUT COUPLING CONTROL INVENTOR Lesier- L.Jon$ g BY g g AT TORNEY$ Aug. 14, 1934. L. JONES 1,970,315

SELECTOR SYSTEM FOR RADIO RECEIVING APPARATUS Filed Dc. 31, 1927 2 SheetsSheet 2 INVENTOR Lesrer L. Jonesv AT ORNEYS Patented Aug. 14, 1934 "PATENTJSOFFICE SELECTOR SYSTEM FOR RADIO RECEIVING APPARATUS Lester L. Jones, omaeugn. J.

Application December 31, 1 27, Serial No. 243,790

22 Claims. (o1. 25o 4o This invention relates to radio receiving appa ratus, and' relates more particularly to radio receiving apparatus in which the selection of the frequencyand the amplification of the energy of the oscillations are effected by different systems;

and. has'special reference to the provision ofucircuit coupling and tuning means in the selector system embodying improvements of the selector system set forth in my copending application Serial No. 205,935 filed July 15, 1927, since issued as Patent 1,350,754, dated March 22, 1932. I The ultimate object of the invention, as set forth in my aforesaid copending application, centers about the provision of a radio receiving'apf .15 paratus in which the selection of the desired frequency is accomplished in geometric progression by means of three or more tuned circuits arranged in cascade, said circuits being devoid of separate energy sources so that the selection of the oscilf 20 lations of the desired frequency is accomplished without energy amplification or relay action, this selective system being so organized that the full geometric selectivity ofthe system is realized or efiectuated. To accomplish this object, I have discovered that the selector system, devoid of electron discharge devices or separate energy sources, should be organized so as to constrain the fiow of energy to move seriatum through the cascaded circuits 53p of the selective system, the said circuits being, moreover, so inter-related as to prevent any but thefirst circuit of the series from receivingenergy frorn an extraneous source. ;I have further discovered that these circuits of theselective sys- V tern may be so coupled together and operated as to effect a maximum energy transfer with a minimum energy loss in the transmission of the energyjand that when so organized a maximum and full geometric selection of the energy is ef- 40 fected. In my aforesaid application Ser. No.

205,935, since issued as Patent 1,850,754, a selector system embodying this organization is described and claimed. I v

The improvements in this selector system which constitute the prime desiderata of my present invention reside in and center about the provision of a simplification of the coupling linkages between the tuned cascadedcircuits, with a consequent simplification of the apparatus and of the energy transfer problems of the system. I have found that the coupling linkages between the circuits of the selector system may be interrelated in a manner to permit that constraining controlof the energy fiow through the sequential 455 circuitsof the system, as well as that coupling control between the circuits, which have been found so desirable in producing the selective energy transmission and the production of the maximum energy transfer with the minimum energy loss aforestated.

H -To the accomplishment of these objects and of such other objects as will hereinafter appear, my invention consists in the elements and their relation one to the other as hereinafter more particularly described and sought to be defined in the claims; reference being had to the accompanying drawings which show the preferred embodiment of my invention, and in which:

. Fig. 1 is a wiring diagrammatic view ofthe improved selector systemof my present invention showingthe same in conventional circuit form,

and

Fig. 2 is a diagrammatic view thereof exemplifying. a preferredmanner of organizing the parts in a commercially built radio receiving set, and l Fig. 3 is a diagrammatic view of of the invention. 4 v i Referring now more in detail to the drawings, the selector system of the invention, generally designated as S, comprises three ormore tuned or selective circuits S1, S2 and S3 coupled together inductively by variable coupling means M1 and M2, the first selector circuit S1 being coupled .to an energy receptor such as the antenna A, and the last selector circuit S3 being coupled to the filament grid circuit of the first tube of an amplifier a.

In order vto realize or effectuate the full selectivity in geometric progression of the selector system S, the selective circuits S1S3 thereof should be so interrelated that the first and third circuitsSl and S3 be capacitively and inductively decoupled, this to constrainthe energy to flow from the first to the thirdselective circuits of the series through the second or intermediate circuit of the series. The three or more cascaded selective circuits should be capacitively or inductively shielded from each other, except through the means M1 and M2 which couple the circuits together, this so thatth-e second and third selective circuits S2 and S3 be prevented from receiving energy from any extraneous source. This inter-circuit shielding or decoupling'except for the energy coupling means between the circuits is found to bevery important in order to obtain the full system selectivity. For producing thatcoupling variation between the circuits which secures the maximum system selectivity with the minimum energy loss in the transmission of the a modification tive and inductive decoupling between the selector circuits of the system. The desired results are preferably secured by localizing :the energytransfer linkages at or in the coupling means M1 and M2, this being desirably obtained-bylocaliz ing the inductive components of the terminal selector circuits S1 and S3 in the inductance coils L and -Lz and ;by subdividing'the inductance of the intermediate circuit S2 into two components L 1 and L22, one foreach of the coupling, means M1 and M ,.the inductive components L21 and L22 being preferably made equal to eachother- For simultaneously adjusting the couplings M1 and M2, the inductive components L21; and L22 of the intermediate circuit, preferably separated a distance apart,,are mounted so as to be movable simultaneously by means of a single control such as into and out'of coupling relation with the inductance coils L1 andLs so that the means for simultaneously. adjusting both of the coupling means M1-and M2 is associated wholly with the secondor intermediate circuit of the series.

.All; of the circuits of-theseries are, preferably made resonant and tunable to the desired selected frequency, the first. selector circuit: S1 being provided for this purpose with theadjustable tuning condenser C1, the 'secondand third selector circuits being correspondingly provided with the tuning condensers C2 and Ca.v Eachof these circuits is preferably grounded as shown by the .conventional grounding &-g. The antennakA, described furthers hereinafter, .is coupled .1capac1 tively by meansof the condenser K to the first tuned-,circuit S1; and where the tuning .con-: densers {C1, C2- and C3 are desired to be simultaneously adjusted for uni-control, the small fixed condensers 11 and. 12 are-arranged in parallel the terminal circuits. Y

T Referring n'owto-Fig; '2 ofthedratvingsj I show thejcircuit' parts described in connection withFig'; 1 arranged in a receiving set assembly for thepurpose of showing some of'the advan- L tages' secured by theorganization of the parts;

the par'ts'of Fig}; of the drawingswhich aresimilar to "Figf lbeing designated by similar reference character's. Thefthre'e fselector. circuits are shieldingly enclosed in vainetal container 13 connectedjto ground andt'o which one of the output leads 14; is connectedgthe input antenna lead 15 and; one of the output,leadsl lfi extending through the shield; for connection to, either the antenna A or Afland to; the amplifier respectively;

To capacitively andinductively shield or decouple the circuits of the series except for the adjustable energy coupling means M1 and M2, the two inductance coils L1 and L3 of the terminal circuits are made astatic and preferably embodying a construction such as is described and claimed in my patent to Coil system, No. 1,608,560 of Nov. 30, 1926, the construction being such that there is substantial freedom from magnetic and electrostatic coupling between these inductance coils. 'These inductance coils L1 and L3, each comprising oppositely wound coaxial coils indicated in both Figs. 1 and 2 and specifically described in my-aforesaid Patent No. 1,608,560, are spaced apart so as to further minimize the effect of anyresidual coupling which may exist therebetween. I have found that the effect of residuals in "a selector system of the kind herein set forth is more severe than in ordinary tuned radio frequency circuits, since there are no separate sources of energy in the selector system S and therefore the energy receivedbythe selector .circuitS3 is of the same order of magnitude as that transmitted by the selector circuit S1; and to produce a substantially complete decouplingso: as to constrainthe energy to flow throughethe intermediate circuitof'the series, I prefer to partition the construction .by'addinga shield plate 17 between the selector circuit S1 and the remainder of :the apparatus and. by interposing a second shield plate 18 capacitively decoupling the tuning-condenser C2 from the tuning condenser C3." The tuning condensers C1, C2 and C3 may be con nected for simultaneous adjustment byhaving the rotors thereof mounted on a single shaft and controlledifrom'a single dial such-as19 also designated as ftuning control.'

For simultaneously adjusting the couplings M1 and--M2, the inductance coils L21 and L22 of the intermediate circuit-located in the compartments of theterminal selector circuits and spaced a substantial'distance apart, are mounted for movement or rotation on. a single tubular shaft 20, the said shaft being desirably utilized as a connecting conductor between the capacitive and inductive components of the intermediate circuit S2, the same being grounded as shown at g. The'other conductive connection 21 "between the coils L21 andL22 of the intermediate circuit is preferably arranged within the tubular shaft 20 and is shielded thereby; To assist in producing the optimum inductive decoupling between the terminal circuits of the series and in further minimizing coupling to external fields which may penetrate the box l3,'the two coils L21 and L22 arepreferably constructed as an astatic pair, this being accomplished by arranging the windings: of these coils in opposite relation or by connecting theterminals of these coils in circuit so as to produce oppositely directed instantaneous magnetic fluxes in the coils L21 and L22.

By means ofthe-construction" thus far described, it will be seen that the inductive components of all {of the three selector circuits are localized in the'twocoupling means M1 and M2, with a resulting simplification not only of the inductance construction of the system,, b ut of the energy-transfer problems between the cir-' cuits. 'It will'then be seen that by making the two inductances L1 and L3 astatic, and the two, inductive componentsof the intermediate circuit as ,an'a'static pair, and by separating these inductancesin themanner set forth, smallresiduals-are produced. and the. effect of-these residuals is further minimized, It will furtherbe seen that to secure the optimum conditions found necessaryin a systemof this character, substantially complete decoupling, both capacitively and magnetically, may be effected by the additional inter-circuit shielding. It will be understood, furthermore, that the coupling control is reduced to or localized in the intermediate circuit S2, resuiting, in further mechanical simplification. It will be further seen that the astatic coils L1 and La are, inelfect, shielded coils and more specifically comprise inductance coils which are almost completely shielded. With this construction the :coil L21 of the intermediate circuit is coupled to the leakage flux of the shielded coil L1 and similarly the coil L22 is coupled in like manner to theshielded coil L2. The coils L21 and L22, how- ..ever, are, substantially completely shielded from each other by the shield plate or partition 17..

With this system it is possible also to arrange the whole coupling means with only one flexible lead, namely, the Wire or conductor 22 joining the tuning condenser C2 andthe coilL22, which flexible lead (at high potential) may be shielded by the grounded shielding tube 23.

As set forth in my aforesaid copending application, it will be further understood that by similarly adjusting the coupling instrumentalities M1 and M2, there is prevented a difference in degree of coupling between the circuits of the series, which difference in degree would result in a loss of selectivity of the system. This will be appreciated when it is seen that when a pair of the circuits is more tightly coupled than another pair, the loss in selectivity of the system due to the tightlycoupled pair is greater than the gain in selectivity which is due to the weakly coupled pair, so that for a given energy transmission the selectivity of the system as a Whole is less than it would be where both pairs of circuits are coupled with equal degrees of coupling. Moreover, by utilizing a plurality of coupling instrumentalitiesand by eifecting the simultaneous adjustment of such coupling instrumentalities, I produce an exceedingly wide coupling and volume range of the circuits. The organization of thecoupling instrumentalities results in that decoupling between the individual circuits which is desired for effecting a constraining of the flow of energy through the consecutive circuits to be progressively acted upon by each of the circuits of the series, this providing the successful solution of the problem of building a selector system which is adapted to produce selectivity in true geometric progression and which is adapted for circuit attachment to a separate audion amplifier system of the untuned type.

The antenna system with which the selector system is employed may be a simple antenna, such asA' heretofore referred to, connected by means of the coupling condenser K to the first selector circuit S1. I prefer, however, to employ an improved antenna system A shown in Figs. 1 and 2 of the drawings, which is described and claimed in an application for Letters Patent filed of even date herewith, SerialNo. 243,789, since issued as Patent 1,761,211, dated June 3, 1930, and which comprises an antenna inductance L made up of two parts 24 and 25 separated by a tap 26 which is connected to a switch means 27, said switch means'being arranged in parallel to the inductance section 25, which latter section is connected to ground 9 by Way of the series tun= 'ing condenser 0. Where the selector system is shielded as shown in Fig. 2 of the drawings, the inductanceL need not be enclosed in a separate metal shield; but where, as shown in'Fig. 1 of the drawings-no separate shield is provided for the selector circuits, the inductance L isenclosed in a separate metal container 28 to'prevent any direct coupling between it and. the intermediate circuitof the series. The tuning of the antenna circuit is accomplished by the rotation ofthe variable condenser C, and this condenser controls the opening and closing of the switch 27 by an element 29 which forms part of the rotor of ,1

the condenser C. During rotation of the, con denser C through one-half of its revolution, element 29'is disengaged from theswitch 27, so that the whole coil L of the antenna is in circuit, and during rotation of the condenser throughthe remaining one-half of its revolution theelement 29 engages the switch 27 to close the same,

as shown in the drawings, and the section 24' only of the antenna inductance L is now in. circuit through the tuning range." With this construction a series tuned antenna may be used efficiently for the entire broadcast receiving range. -.f.

As an example of suitable magnitudes which may be employed for the constants of the circuits to produce the intended results, themaximum capacity of the antenna tuning condenser C may be micro-micro-farads, the. maximum capacity of the tuning condensers C1, C2 and C3 may be 500 micro-micro-farads, the capacity of, the

coupling condenser K may be 3 micro-microfarads, the. antenna inductance L may be 1 .1 milihenrys; the astatic coils L1 and Ls are equalzto each other and equal to the sum of the astatic pair of coils L21 and L22, and the mutual inductances of M1 and M2 are equal to oneanotherfor all settings.

In Fig. 3 I show a modified form of theinvem tion in which four tuned circuits in lieu ofthree timed circuits are employed. To accomplish this the intermediate circuit S2 is subdivided intotwo similar tuned circuits. The first and third OI'BX'. ternal circuits S1 and 53 are substantially the same as that shown in Fig. 1 of the drawings, and are indicated by similar reference characters.

The inductive component of the intermediate cire cuit S2 is subdividedin substantiallythe same manner as that heretofore describedgbut the same is subdivided into componentsfor the .two tuned circuits. Thus the inductive component of vided into the two inductance coils L21 and L22, the first for the coupling M1 and the second for the coupling M2, the inductive component, how.- ever, being further provided with two coils L and L which are small fractions of the inductance of the coils L21 and L22 and are coupled very tightly together on the shaft 20, which shaft is connected to the coils L21 and L22 in-the man'- ner disclosed in Fig. 20f the drawings. The connections between all of the coils in this intermediate circuit are fully indicated in Fig. .3 of the drawings, and as shown, the coils, L and L are inductively but may be conductively coupled and other coupling units.

" The two tuned circuits for the generalizedin These coilsL and Lb this generalized. intermediate circuit S2 is subdil 5 terr'nediate circuit S2 are provided by the tuning condenser'czi associated with the coil L21 and the tuning condenser Caz-associated with the coil L22; -The circuitconnections are as -shown in Fig.3 of the drawings, and similarto'that heretofore described; For" the reasons'aforestatcd, the small-condensers 12a .and 121) are connected-in parallelwith-these tuning condensers, 'The opera-tion of the selector system of my present-invention and the many advantages thereofwill' in'the -main be fully apparentfrom the above"*detailed description thereof. It will be further apparent that while-I have shown and described my invention in its preferred form, many changes and modificationsmay bemade in the structure disclosed without departing from the spirit of my inven tion, defined in the following claims;

'lclainiz- 1 -'-l.' A "system for selec'tingin geometric progression electrical oscillations of a given frequency froinoscillations diifering therefrom in frequency comprising at least three circuits of low decrement resonant'to the frequency of the oscillations to be selected and arranged in cascade or series;'a first coupling means linking the first circuit ofthe series to the second or intermediate circuit solely by leakage flux for the transfer to the second circuit of energy selected by the first circuit, and'a second couplingmeans linking the second or intermediate circuit of. the series to th'ethird circuit solely by leakage flux for the transfer to the third circuit of energy selected by the second circuit, the inductive components of said first and thirdcircuits being substantially localized respectively in said first and second coupling means and the inductance of said intermediate'circuit being divided into two components, one component for each of the said coupling means; I t

i 2. A system for'selecting ingeometric progressionelect'rical oscillations of a given frequency from" oscillations differing therefrom in frequency comprising at least three circuits of low decre- V -5 mentresonantto the frequency of the oscillations to be" selected and arranged in cascade or series, aifirst variable coupling means linking the first circuit of the series to the second or intermediate circuit solely byleakage fiux for the transfer to the second'circuit of energy selected by the first circuit, a second variable coupling'means linking the second or intermediate circuit of the series to the third circuit solely by leakage flux for the transfer to'the third circuit of energy selected by the second circuit, the inductive components of sai'dfirst and thirdcircuits being substantially lo- 'calized in said coupling means and the inductance of said intermediate circuit being divided into two components, one component for each of thesaid coupling means, and means for simultaneouslysimilarly adjusting'both of said variable coupling means.- I 33A system for selecting in geometric progress'ion electrical oscillations of a given frequency from oscillations differing therefrom in frquencycomprising at least three circuits of low decrement, resonant to the frequency of the oscillations'to be selected and arrangedin cascade or series, a first coupling means linking the first circuit of the series to the second or intermediate, circuit solely by leakage fiuk for the transfer to the second circuit of energy. selected byfthe ifirst circuit, a second coupling means linkingthe'second or intermediate'circuit of the. series to the third circuit solely by leakage flui';

for the transfer to thesthird circuit of energy selected by the second circuit; the inductiveicom-i ponents of said first and third circuits being substantially localized in said coupling 1 means and the inductance of said'intermediate circuit being divided into two equal and separated-components, one component-for each oflthe i said coupling'means, and means for tuning each of said circuits.

4. A selective system comprising at leastthree circuits of low decrement arranged in cascade or series and-tunable to a given frequencyof oscillation, a first coupling means linking the first circuit of the series to the second'orintermediate circuit, said first coupling-means comprising'a substantially astatic inductance coil-"in the fir'stcircuit and a coil in thesecond circuit linked thereto solely by leakage flux, a second coupling means linking the second-or intermediate circuit of the series to the third circuit, the said second coupling means comprising-a substantially astatic coil in said third circuit and'a second coil in said intermediate circuitlinked thereto solely by leakage flux, the inductances of the two coils of the intermediate circuit being substantially equal.

5. A selective system comprising at least three circuits of low'decrement arranged in cascade or series and tunable to a given frequency of oscillation, a first variable couplingmeans linking the first circuit of the series tothe second or intermediate circuit, said first coupling means comprising a substantially astatic inductance coil in the first circuit and a coil in the second circuit linked thereto solely by "leakage flux a second variable coupling means linking the see ond-or intermediate circuit of the series tothe third circuit, the said second coupling means comprising a substantially astatic'coil in said third circuit and a second coil in said intermedi ate-circuit linked thereto solely by leakage'fiux, the inductances of the two coils ofthe intermediate circuit being substantially equal, and means for simultaneously and equally adjusting both of said variable coupling means.

6. A selective system comprising at least three circuits of low decrement arranged in cascade 'or series and tunable to a given frequency of oscillation, a first coupling means linking the-first circuit of the series to the second or intermedi ate circuit, said first coupling means' comprising a substantially astatic inductance coil in the first circuit and a coil in the second circuit linked thereto solely'by' leakage flux, a second coupling means linking the second or intermediate circuit of the series to the third circuit, the said second coupling means comprising a substantially astatic coil in said third circuit and'a second-coil in said intermediate circuit linked thereto solely by leakage flux, the inductancesof the two-coi1s of the intermediate circuit being substantially equal andthe' inductance of said first and third circuits being substantially localized in said astatic coils.

7. Aselective system comprising at least three circuits of low decrement arranged in cascade or series and tunable to a given frequencyof oscillation, a first coupling means linking the first circuit of the seriesto the second or intermediate circuit, said first coupling means comprising a substantially astatic inductance coil-in the first circuit and a coilin the second circuit linked thereto, a second coupling means linking the second or intermediate circuitof theseries to the third circuit, thesaid secondcoupling means field. V 10. A selective system comprising a plurality of tuned circuits arranged in series andincluding comprising a substantially astatic coil in said third circuit and a second coil in said intermediate circuit linked thereto, the two coils of the intermediate circuit comprising in combination an inductance astatic with respect to the signal wave field.

8. A selective system comprising at least three circuits arranged in cascade or seriesand tunable to a given frequency of oscillation, a first variable coupling means linking the first circuit of the series to the second or-intermediate circuit, said first coupling means comprising a substantially astatic inductance coil in thefirst circuit and a'coil in the second circuit linked thereto, a second variable coupling means linking'the sec-' nd or intermediate circuit of the series to the third circuit, the said second coupling means comprising a substantially astatic coil in said third circuit and a second coil in said intermediate circuit linked thereto, the twocoils of the intermediate circuit comprising in combination an inductance astatic :with respect to the signal wave'field and being equal in inductance, and means for simultaneously and equally moving 11 said astaticpair of coils to simultaneously'adjus't both of said variable coupling means. a

9. A selective system comprising a plurality of tuned circuits arranged in series and including terminal circuits and an intermediate circuit, and means for linking said intermediate circuit to said terminal circuits comprising a pair of spaced apart inductance coils one in each of said terminal circuits and a pair of inductance coils in said intermediate circuit spaced apart and 'I coupled to the aforesaid inductance coils of said terminal circuits, said pair of coils in the intermediate circuit comprising in combination an inductance astatic with respect to the signal wave terminal circuits and an intermediate circuit and means for linking said intermediate circuit to said terminal circuits comprising two spaced apart inductance coils one in each of said terminal circuits and a pair of inductance coils in said intermediate circuit spaced apart and coupled to the inductance coils of said terminal circuits, and means connecting the said pair of inductance coils, said connecting means consisting of a tubular shaft connected in grounded circuit with the coils and a connecting conductor within said tubular shaft.

11. A selector system comprising at least three circuits of low decrement resonant to the frequency of the oscillations to be selected and arranged in cascade or series, each of said circuits embodying inductance and capacity components forming a closed oscillating circuit, a first coupling means linking the first circuit of the series to the second or intermediate circuit solely by leakage flux for the transfer to the second circuit of energy selected by the first circuit, a second coupling means linking the second or intermediate circuit of the series to the third circuit solely by leakage flux for the transfer to the third circuit of energy selected by the second circuit, the inductive components of the first and third circuits being substantially localized respectively in said first and second coupling means, and means for simultaneously adjusting the tuning of said three resonant circuits.

12. A selector system comprising at least three circuits of low decrement resonant to the frequency of the oscillations to be selected and arranged in cascade or series, each of said circuits embodying inductance and capacity components forming a-closed oscillating circuit, a first 'coupling means linking the first circuit of the series to the second or intermediate circuit solely by leakage flux for the transferv to the second circuitof energy selected by the first circuit} asmall seriescondenser for loosely capacitively coupling the first circuit of the series toan energy receptor, a second coupling means linkingthe. second or intermediate circuit of the series tothe third circuit solely by leakage flux for the transfer to thethirdcircuit of energy selected by the second circuit, the inductive components o'f'the' first and third circuits being substantially: localized respectively in said first and second coupling means and the inductance of said intermediate circuit being divided into two compo ne'nts, one component for each of said coupling means, and means for simultaneously adjusting the tuningof saidthree'resonant circuits.

13. The selector system of'claim 11 in which the capacity components of the three circuits comprise the tuning means, and con der'tlsersin parallel with the capacity tuning means of the first and seco'ndcircuits to' raise theminimum circuit capacity thereof byan amount equal to the tube input capacity of a tube to which the third circuit of theseries is connectible.

14. A system for 'sele'cting electrical oscillations of a givenf'requency from oscillationsdiifering therefrom in frequency comprising four closed circuits of low decrement resonant to the frequency of the oscillations to be selected and arranged in cascade or series, each of said circuits embodying capacitive and inductive components, a first energy transfer inductive coupling means linking the first circuit of the series to the second circuit, a second energy transfer inductive coupling means linking the third circuit of the series to the fourth circuit, and energy transfer means coupling the second and third circuits together, the inductive components of all of the four circuits being substantially localized in said first and second inductive coupling means.

15. The system of claim 14 in which the energy transfer means coupling the second and third circuits together comprises inductance'elements tightly coupled together having avalue which is a small fraction of the inductance magnitude of the second and third circuits, thereby providing only a loose coupling between the circuits, despite close juxtaposition of the inductance elements.

16. The system of claim 14 in which the inductive components of the first and fourth circuits are substantially astatic coils, whereby the coupling thereto is solely by means of leakage flux.

17. A selective system comprising at least three circuits arranged in cascade or series and tunable to a given frequency of oscillation, a first coupling means linking the first circuit of the series to the second or intermediate circuit, said first coupling means comprising an almost completely shielded inductance coil in the first circuit and a coil in the second circuit coupled to the leakage flux of the shielded coil, a second coupling means linking the second or intermediate circuit of the series to the third circuit, the said second coupling means comprising an almost completely shielded inductance coil in said third circuit and a second coil in said intermediate circuit linked thereto.

18. A selective system compriisng at least three circuits arranged in cascade or series and tunable to a-given frequency of oscillation, a first cou-' pling means linking the first circuit of'theseries to the second/or intermediate circuit, saidifirst coupling means'comprising an almost completely shielded inductance coil in the first circuit and acoilin the secondcircuit linked to the leakage flux of the shielded coil, a second coupling means linking the second or intermediate circuit; of the seriesto the third circuit, the said second C0115 pling-means comprising. an almost completely shielded inductance coil in said third circuit and arsecond coil in said intermediate circuit linked thereto, and means for substantially completely shielding-the'two coils of the intermediate circuit'from eachother.

-:19-. The system of claim 14 in which each of the four circuits is a closet tuned circuit the firstzone of which 'iscombined with a small'se-, rieszcondenser for loosely capacitively coupling thefirst closed tuned circuit to an antenna.

20. The system of claim" 1.41m which the first andsecond energy transfer coupling means each comprises. inductance coils at least one of which is so shielded f that the inductance coils are coupled :solely by leakage flux and in whichrthe inductance coils of the secondand=third circuit are :substantially completely -ma gnetically '-de-- coupled one from the other. c a

21. The, system of claim--l4-in-which thefirst andsecond energy transfer coupling means each comprises inductance coils at least one of which is so shielded that the said inductance coils are coupled solelyrby leakage flux, in which the in-. ductance coilsof the second and third circuits are substantially completely magnetically .de' coupled one. from the other, and'in which the energy transfer means coupling the second andthird circuits togethercomprises aninductance coilwhich is a small fraction of the inductance magnitude of the second and-third circuits and which tightly couples a portion of one of'these circuits to the other.

-22. A system for selecting electrical: oscilla. tions'of a given frequency from oscillations differing therefrom in frequency comprising four,

f LESTER L. JONES. 

